Conditionally render MCP guideline sections

[Xiol]

Before this change, the Tools and Searching Documentation sections were always emitted into the generated AI guidelines, even when users chose not to enable MCP during installation. This meant AI agents were instructed to use database-query, search-docs, and other MCP tools that simply weren't available in their environment, leading to failed tool calls or confusing behaviour.

After this change, those sections are only included when MCP was actually selected at install time. Users who run a guidelines-only setup get a leaner, accurate guideline file that reflects their actual configuration.

Closes #721.

[pushpak1300]

Hey! Nice PR, clean and follows the existing patterns well.

One thing I noticed, when boost:update regenerates guidelines, it calls InstallCommand with --guidelines and --skills but never passes --mcp. Since selectBoostFeatures() only returns explicitly passed flags, hasMcp will always be false during updates. This means existing MCP users who run boost:update would silently lose the ## Tools and ## Searching Documentation sections even though their MCP server is still configured.

[Xiol]

Thanks for your review, good catch there! I'm now passing the --mcp flag from UpdateCommand to InstallCommand during boost:update, so the MCP sections are retained.

[pushpak1300]

But MCP config once published isn't supposed to change. it will be kind of breaking change,

[Xiol]

How about this? I've updated buildGuidelineConfig() to fall back to the stored config value when MCP isn't in the selected features. This way the guideline sections are preserved during updates without re-triggering MCP installation.